I didn't want to appear to be ignoring your question, so am replying. However, as a casual observer I must say that I can't answer with any degree of expertise.But City are being charged over rules that didnt exist at the time, hence the joke of 115 charges. So why not Chelsea ?
My instinct is that trying to justify City's position based upon a comparison with Chelsea's isn't going to be very productive. I suspect that from a legal perspective it's like comparing apples to oranges.